93 ZJ Heater Motor

You are likely describing a blower motor that has worn out.

They start to draw too much power and usually blow out the resistor pack first, this kills low speeds, then they work on the direct high speed wire until they melt down and usually smoke out the heater switch or heater relay, then they sometimes have the grace to die.

I normally try direct power to the motor to see if it has been put out of my misery and if it is dead, then I change it and the resistor pack.

A meter can tell you if the switch has melted down or not. I put the meter on the plug for the heater and try the switch. If it only works in high, then the resistor pack is dead. If it works in all settings, you got really lucky. If it sends no power, there might be a relay to change with the relay right beside it for a test to see.

If you change the relay and still no power, suspect the switch has melted.

Mike

There is no vacuum involved. There is a resistor that controls the speed of the motor. That's the first thing the manual tells you to check when the motor doesn't operate at the selected speed. You need to run the on-board diagnostics if you have ATC.

Dick

Great information. Thanks so much. Guess I'll find a cozy garage and grab my meter. Thanks again.

D did pass the time by typing:

Do you have the schematic? I can scan it for you if you need them.

Automatic or manual AC?

D did pass the time by typing:

You could do what I used to do. Get some tarp and a few pieces of pvc pipe and make a shelter to block the wind. I worked on the engine of my old Chevy that way. Still not nice and warm but a few strategically placed clamp on lamps kept the chill off.

D did pass the time by typing:

That would be my thought. Either burning out or caked up with crud.

Another possiblity, kinda remote since it usually happens much earlier is the insulation strips used to connect hoses in the AC system have worked loose and fell into the fan cage. That can bind it up nicly. You will know when you drop the motor.